Project Number: 8010-22000-029-11-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Sep 1, 2015
End Date: Aug 31, 2020
To test for virulent genotypes of soybean aphid in field experiments on the impact of the introduced parasitoids, Aphelinus glycinis and Aphelinus rhamni, and soybean resistance on the abundance and dynamics of soybean aphid.
To establish the parasitoids Aphelinus glycinis and Aphelinus rhamni on soybean aphid, we will release large numbers at 2-4 locations in Iowa. At the Beneficial Insect Introductions Research Unit, Newark, DE, we can rear over 240,000 parasitoids every 3 weeks or 640,000 over the growing season, using protocols we have already developed. We will release parasitoids in fields where host plant resistance trials are being carried out. Breeders have developed several isogenic lines with one, two and three Rag genes. We will test the impact on parasitism and soybean aphid abundance of isogenic lines with either no resistance or combinations of Rag1, Rag2, and Rag3 genes, including a triple pyramid of Rag1+Rag2+Rag3, on soybean aphid. The set of plots with each resistance genotype will be replicated, and either naturally or artificially infested with soybean aphid. We will release A. glycinis and A. rhamni in half of the replicates and measure the impact on soybean aphid densities. This will allow us to determine the interaction between Rag genes and parasitoids in their impact on soybean aphid abundance. We will monitor A. glycinis by sampling in soybeans at the release sites and in buckthorn stands near release sites. We will collect data on soybean aphid and parasitoid densities and the impact of the parasitoid with whole-plant samples for soybean and branch samples for buckthorn. We will sample aphids and parasitoids randomly along transects across each field on each sample date. To estimate aphid and mummy density, we will photograph leaves for later counting, and we will also collect aphids and mummies from plants. We will pool healthy aphids by field and rear them to determine whether they were parasitized and by which species. These samples will be shipped to Dr. Michel's laboratory for molecular analysis. We will determine dispersal patterns and prevalence of virulent genotypes using alate soybean aphids from soybean and buckthorn during spring dispersal from buckthorn, summer dispersal among fields, and fall dispersal to buckthorn. DNA will be extracted, PCR amplified, and genotyped by sequencing, which will provide data for population structure analysis, estimation of virulence frequencies, and identification of parasitoids to species. Data analysis on aphid population structure and migration will be performed with BAMOVA, which uses phi and FST statistics, designed for calculating the partitioning of genetic variation among populations using sequence-based markers.